84 lines
2.5 KiB
JavaScript
84 lines
2.5 KiB
JavaScript
'use strict';
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Object.defineProperty(exports, '__esModule', { value: true });
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var base = require('./base.cjs');
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var coord = require('./coord.cjs');
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var nutation = require('./nutation.cjs');
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var solar = require('./solar.cjs');
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/**
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* @copyright 2013 Sonia Keys
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* @copyright 2016 commenthol
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* @license MIT
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* @module eqtime
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*/
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const { cos, sin, tan } = Math;
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/**
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* e computes the "equation of time" for the given JDE.
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*
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* Parameter planet must be a planetposition.Planet object for Earth obtained
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* with `new planetposition.Planet('earth')`.
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*
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* @param {Number} jde - Julian ephemeris day
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* @param {planetposition.Planet} earth - VSOP87 planet
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* @returns {Number} equation of time as an hour angle in radians.
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*/
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function e (jde, earth) {
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const τ = base["default"].J2000Century(jde) * 0.1;
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const L0 = l0(τ);
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// code duplicated from solar.ApparentEquatorialVSOP87 so that
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// we can keep Δψ and cε
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const { lon, lat, range } = solar["default"].trueVSOP87(earth, jde);
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const [Δψ, Δε] = nutation["default"].nutation(jde);
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const a = -20.4898 / 3600 * Math.PI / 180 / range;
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const λ = lon + Δψ + a;
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const ε = nutation["default"].meanObliquity(jde) + Δε;
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const eq = new coord["default"].Ecliptic(λ, lat).toEquatorial(ε);
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// (28.1) p. 183
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const E = L0 - 0.0057183 * Math.PI / 180 - eq.ra + Δψ * cos(ε);
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return base["default"].pmod(E + Math.PI, 2 * Math.PI) - Math.PI
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}
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/**
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* (28.2) p. 183
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*/
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const l0 = function (τ) {
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return base["default"].horner(τ, 280.4664567, 360007.6982779, 0.03032028,
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1.0 / 49931, -1.0 / 15300, -1.0 / 2000000) * Math.PI / 180
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};
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/**
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* eSmart computes the "equation of time" for the given JDE.
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*
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* Result is less accurate that e() but the function has the advantage
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* of not requiring the V87Planet object.
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*
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* @param {Number} jde - Julian ephemeris day
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* @returns {Number} equation of time as an hour angle in radians.
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*/
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function eSmart (jde) {
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const ε = nutation["default"].meanObliquity(jde);
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const t = tan(ε * 0.5);
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const y = t * t;
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const T = base["default"].J2000Century(jde);
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const L0 = l0(T * 0.1);
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const e = solar["default"].eccentricity(T);
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const M = solar["default"].meanAnomaly(T);
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const [sin2L0, cos2L0] = base["default"].sincos(2 * L0);
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const sinM = sin(M);
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// (28.3) p. 185
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return y * sin2L0 - 2 * e * sinM + 4 * e * y * sinM * cos2L0 -
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y * y * sin2L0 * cos2L0 - 1.25 * e * e * sin(2 * M)
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}
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var eqtime = {
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e,
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eSmart
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};
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exports["default"] = eqtime;
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exports.e = e;
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exports.eSmart = eSmart;
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